Processing of substrates (e.g., semiconductor, glass, etc.) for use in electronic devices is typically done in one or more processing chambers of a processing tool. The substrates may be moved between the processing chambers via a central transfer chamber. A slit valve connects the central transfer chamber to a processing chamber. Robot arms rotate and extend to load and unload the substrate wafers from the processing chambers. The substrates must be precisely positioned on the robot arms (or blades) in ideal pickup and drop positions. Deviations from these ideal positions may create negative consequences later in the processing of the substrates. For example, if the substrates are not properly positioned and seated on the robot arms at the time of pickup, the substrates may slide off the arms during withdrawal from the processing chambers. This may result in the substrate being partially left on the processing chuck and partially in the slit valve, thereby requiring venting and opening of the transfer chamber to manually remove the substrate. Additionally, the substrate may be contaminated, damaged or even broken, by contact with the chamber parts or motions of the slit valve, particularly if the valve is closed prematurely. These negative consequences may result in longer and more expensive processing times, which is undesirable.
Conventional systems for precisely positioning the substrates include using specialized setup tools and measurement wafers (such as “camera on wafer”) to program the rotation and extension of the robot arms when loading or unloading the substrates from the processing chambers. However, some of the problems with these systems are that either the chambers must be opened to use the tools, or the tools themselves are extremely expensive and therefore may be quite limited in usage.
Additionally, the robots experience normal wear, particularly at the bearings, as well as changes in temperature, which will therefore cause the robot components to expand and contract. Thus, the “ideal” pickup and drop positions for the substrate in the chamber change over time. However, if the extension and rotation of the robot arms are set to a particular measurement, as described by conventional systems, these set measurements do not account for these changes in the tools.
Moreover, as the substrates are in transit, the substrates themselves may shift on the arms, or move in the chambers as they are lowered onto or lifted from processing chucks and other apparatus. Robots having particularly calibrated extension and rotation movements are unable to adjust for these misplacements of the substrate on the robot arm. Accordingly a need exists for a system that allows for improved substrate centerfinding.